In facilities such as offices, houses, and the like, in order to efficiently equalize electric power consumption or realize electric power savings, it is necessary to recognize electric power consumed in the facilities. As a method for realizing the measurement of electric power consumed in a facility, there has been known a method in which the electric power consumption of each load (a personal computer, an air conditioner, a refrigerator, and the like) connected to an existing power distribution network is measured using an electric-power sensor. As such a method as described above, for example, a method may be cited in which, using electric-power sensors provided between outlets provided in a power distribution network and all loads connected to the outlets, the amounts of electric currents flowing into the loads and the voltages at positions to which loads are connected are measured, and hence total electric power consumption in the facility is obtained on the basis of the electric power measurement results for all loads.
However, in such a method as described above, since electric-power sensors are connected to all loads in the facility, an installation cost increases. Therefore, the method is not realistic. Accordingly, there has been known a technique in which total electric power consumption in a facility is estimated on the basis of information obtained from electric-power sensors connected to some loads in the facility, so as to reduce an installation cost for electric power consumption measurement.
For example, a method or the like has been proposed in which, by using electric-power sensors, the voltage values at positions to which loads are connected are measured, and total electric power consumption in a facility is estimated. Focusing on a system included in a power distribution network, the amount of a voltage drop and the conductor resistance value of an electric wire, which lead up to a position to which an electric-power sensor is connected, are measured. Accordingly, the amounts of electric currents flowing into the loads connected to the system are estimated, and electric power consumption is estimated on the basis of the estimated amounts of currents. After that, by summing the estimated amounts of electric power consumption in individual systems for all systems, electric power consumption in the entire facility is estimated. In addition, the term “system” means each of circuits included in a power distribution network used for receiving generated electric power from a power transmission network and distributing the electric power, and means each of circuits branching from a trunk line.
The method mentioned above will be described with reference to FIG. 1. FIG. 1 is a schematic view illustrating a power distribution network that distributes electric power, received from a power transmission network, to loads connected to a system 1 and a system 2. A transformer T1 is, for example, provided on a distribution board, the primary side input of the transformer T1 is connected to the power transmission network, and a consumer-side power distribution network is connected to the secondary side output thereof. Resistances r1 to r8 indicate the conductor resistances of circuit wiring lines. Branching in FIG. 1 indicates the branching of a trunk line, and corresponds to, for example, a branch circuit such as a distribution board when house wiring is assumed. In addition, an outlet C1 is provided in the system 1, and a load F1 is connected to the outlet C1 through an electric-power sensor Se1. An outlet C2 and an outlet C3 are provided in the system 2, a load F2 is connected to the outlet C2 through an electric-power sensor Se2, and a load F3 is connected to the outlet C3 through an electric-power sensor Se3. Focusing on the system 2 included in the power distribution network, the amount of a voltage drop and the conductor resistance value of an electric wire, which lead from a position to which the electric-power sensor Se2 is connected up to a position to which the electric-power sensor Se3 is connected, are measured. Next, the amounts of currents flowing into all loads connected to the system 2 are estimated, and electric power consumption is estimated on the basis of the estimated amounts of currents. After that, with respect to the system 1, electric power consumption is also estimated, and, by summing the estimated amounts of electric power consumption for all systems, total electric power consumption in the facility is estimated.
However, in order to realize such an electric power estimation method as described above, it is necessary to recognize which position in the power distribution network the electric-power sensor is connected to, and recognize a positional relationship between the electric-power sensors. Namely, it is necessary to recognize which system the electric-power sensor is included in. However, when the administrator of a power distribution network and a person in charge of electric power monitoring are different from each other, or in an old facility in which a power distribution network is not managed, it may turn out that it is difficult to recognize the configuration of the power distribution network to be a target of monitoring. In such a case, even if an electric-power sensor is provided for a load, it may turn out that it is difficult to recognize which position in the power distribution network the electric-power sensor is provided at. In addition, it is necessary for the outlet C2 and the outlet C3 to be adjacent to each other in the system, and it is necessary for no load to be located between the outlet C2 and the outlet C3. Namely, when another load is located between the outlet C2 and the outlet C3, it is difficult to obtain adequate accuracy for the estimation of electric power consumption, owing to the effect of the other load.
Accordingly, there has been known a method in which electric-power sensors mutually transmit and receive to and from each other power-line superimposed signals. For example, by measuring the voltages and currents of signals, individual electric-power sensors calculate the phase differences therebetween, and a positional relationship between the electric-power sensors in a system is estimated on the basis of the power flow directions of the signals. An example of the method is disclosed in Japanese Laid-open Patent Publication No. 11-308787. However, in this method, since an electric-power sensor that can cause a signal to flow in an electric wiring line in a power distribution network and measure the amount of a current flowing in an electric wire in the power distribution network is necessary, an installation cost increases.